The proposed study will examine several important issues which must be addressed in order to restore movements involving the wrist, elbow, and shoulder joints in C4-C7 quadriplegics using electrical stimulation of the muscles acting at these joints. The first issue that the mechanical effects (e.g., force) produced by the individual stimulation of each muscle acting at these joints must be known. A robotic manipulator will be used to experimentally determine the force and impedance components produced at the hand by individual paralyzed muscles for different levels of stimulation intensity and for various hand locations in space. The second issue to be addressed is how to best select a combination of muscles to stimulate to restore a specified task, since different combinations of muscles can often achieve the same behavior. The third issue to be addressed is how to specify desirable mechanical properties for movements to be restored by electrical stimulation.